1. Field of the Invention
The present invention relates to the art of processing image data representing an image taken by an image-taking device, and particularly to the art of processing a plurality of batches of image data respectively representing a plurality of images which are taken by one or plural image-taking devices from an object a whole image of which cannot be taken at once by the one image-taking device or each of the plural image-taking devices.
2. Discussion of Related Art
There is known an electric-component (EC) mounting apparatus which includes a suction nozzle for holding an EC, and an image-taking device for taking an image of the EC held by the nozzle and thereby inspecting a condition of the EC. The image-taking device may be a CCD (charge-coupled-device) camera including a matrix of CCDs for taking a whole image of the EC. Necessary information can be obtained from the taken image of the EC.
However, when a commonly or widely used CCD camera including a limited number of CCDs or having a limited number of pixels takes, at once, a whole image of a large-size EC having a complex shape, each of the CCDs must take a pixel image of an excessively large portion of the EC, which leads to lowering the degree of resolution of the taken image. Thus, it is difficult to recognize accurately one or more fine portions of the EC, such as its lead wires.
Hence, a camera including a single array of CCDs, i.e., a xe2x80x9clinexe2x80x9d sensor (hereinafter, referred to as the line-sensor camera) has been used in place of the CCD camera. The line-sensor camera is allowed to have a greater number of CCDs or pixels per unit length, than the CCD camera including the matrix of CCDs. Thus, each of the CCDs of the line-sensor camera has only to take a pixel image of a smaller portion of the large-size EC, which leads to improving the degree of resolution of the taken image. However, the line-sensor camera itself is expensive, and additionally needs a special high-performance light source, which leads to increasing the overall cost of the EC mounting apparatus which employs the line-sensor camera. Moreover, the line-sensor camera needs a longer time to take the whole image of the EC.
In this background, there has been proposed another method using the CCD camera. In this method, as shown in FIG. 14, respective images of a plurality of portions or parts (i.e., four corners) 202 of a large-size EC 200 as an object are sequentially taken by a single CCD camera, or are simultaneously taken by a plurality of (i.e., four) CCD cameras, and a plurality of batches of part-image data representing the respective images of the plurality of parts 202 of the EC 200 are obtained. First position data representing respective positions of the four parts 202 in the EC 202 are obtained from the batches of part-image data, and second position data representing a position of the large-size EC 202 as a whole are obtained from the first position data.
However, in the above method in which the plurality of batches of part-image data are obtained by one or more CCD cameras, a whole or complete image of the large-size EC 200 is not taken. Therefore, the prior method cannot inspect the EC 200 as a whole.
It may be possible to obtain a whole image of the large-size EC 200 by first taking, with one or more CCD cameras, a plurality of part images from a plurality of parts of the EC 200 and then connecting the taken part images to each other while taking into account respective relative positions of the CCD camera or cameras relative to the EC at respective times when the part images are taken. In fact, however, an image-taking device (e.g., a CCD camera) has a distortion of a lens (e.g., a distortion of a matrix of CCDs) and accordingly an image taken by the image-taking device may have distortions in its peripheral portions, in particular. In addition, physical relative positions of the image-taking device or devices relative to the EC 200 may contain some positional errors from reference or prescribed relative positions. If the part images taken from the EC 200 are connected to each other without taking into account the lens distortion or the positional errors, then it would be difficult to reproduce an accurate, whole image of the EC 200 because of the distortion and the errors.
Though the above discussion relates to the art of taking and processing images of ECs, the above problems may occur to not only the ECs but also other sorts of objects (e.g., connectors).
The present invention provides an image processing method, an image processing system, and a modifying-data producing method which have one or more of the following technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (21). Any technical feature that includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to the latter feature. However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited. In addition, in the case where one technical feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed. That is, it is possible to select and employ only a portion (one, two, . . . , but not all) of those items.
(1) According to a first feature of the present invention, there is provided a method of processing a plurality of batches of object-part-image data representing a plurality of object-part images which are taken by at least one image-taking device from a plurality of parts of an object, respectively, and thereby obtaining at least one optical characteristic value of the object, the object-part images imaging the parts of the object such that at least one first object-part image images at least one first part and at least one second object-part image images at least one second part adjacent to the at least one first part in the object and includes at least one overlapping portion imaging a portion of the at least one first part, each of the plurality of batches of object-part-image data comprising a plurality of optical characteristic values respectively associated with a plurality of physical positions, and thereby defining a corresponding one of a plurality of physical screens, the method comprising the steps of designating at least one virtual position on a virtual screen corresponding to the parts of the object, modifying, based on predetermined modifying data, the at least one virtual position on the virtual screen, and thereby determining at least one physical position corresponding to the at least one virtual position, on one of the physical screens, and obtaining at least one optical characteristic value associated with the at least one physical position on the one physical screen, as at least one optical characteristic value associated with the at least one virtual position on the virtual screen and as the at least one optical characteristic value of the object. At least one first part of the object may belong to a first column of a matrix of parts of the object, and at least one second part of the object may belong to a second column of the matrix that is adjacent to the first column in the matrix.
In the present image processing method, a plurality of object-part images are taken from a plurality of parts of an object, and a condition of the object as a whole may be obtained based on a plurality of batches of object-part images representing the taken object-part images, and the modifying data. A virtual position, designated on a virtual screen, where an optical characteristic value of the object is to be obtained, is modified to a physical position corresponding to the virtual position, on an appropriate one of a plurality of physical screens. Even if each of the physical screens may have a distortion and/or there may be a relative-positional error between the object-part images, the modifying data reflecting the distortion and the relative-positional error are used to determine the physical position accurately corresponding to the virtual position on the virtual screen, and an optical characteristic value associated with the physical position is determined as the optical characteristic value associated with the virtual position, that is, as the optical characteristic value of the object. A group of combinations each of which consists of a virtual position and a corresponding optical characteristic value each obtained in this manner, provides, on the virtual screen, a batch of image data representing the object-art images connected to each other such that the connected, integral image is free of the distortion or the relative-positional error.
The present method allows a commonly or widely used image-taking devices to take not only images of a small-size or medium-size EC but also images of a large-size EC, which contributes to reducing the cost needed to carry out the method.
However, it is not essentially needed to reproduce, on the virtual screen, a whole image of the object, but it is possible to reproduce, on the virtual screen, only an integral image of a desired portion of the object. More specifically described, it is possible to designate a portion on the virtual screen and obtain at least one optical characteristic value corresponding to the designated portion. In this case, the amount of processing of the image data is reduced as such, and accordingly the amount of calculations needed to process the image data is likewise reduced. The virtual position designated on the virtual screen may be a position where a xe2x80x9cseekxe2x80x9d line intersects a boundary line of each part of the object in the corresponding object-part image, i.e., a position of an xe2x80x9cedgexe2x80x9d point where respective optical characteristic values of respective points on the seek line most greatly change.
The predetermined modifying data may be modifying data which are produced, in advance, by a modifying-data producing method, described later. When the virtual position is modified based on the modifying data and a physical position corresponding to the virtual position is determined, it is possible to either modify a virtual area corresponding to an image-taking element of the image-taking device, on the virtual screen, and thereby determine a physical area on an appropriate one of the physical screens, or modify a virtual set of coordinates indicating an arbitrary virtual point on the virtual screen, and thereby determine a physical set of coordinates indicating a corresponding point on an appropriate one of the physical screens.
The optical characteristic value may be any sort of value which is characteristic of an optical property of the object, such as luminance or hue. Each optical characteristic value may be expressed in terms of binary values or 2 steps, or 256 steps.
(2) According to a second feature of the present invention that includes the first feature (1), the image-taking device includes a plurality of image-taking elements, the each batch of object-part-image data comprises the plurality of optical characteristic values which are, on the corresponding physical screen, associated with respective physical pixel areas corresponding to the plurality of image-taking elements of the image-taking device, and the modifying data comprise data which associate respective virtual pixel areas on the virtual screen, with the respective physical pixel areas, on each of the physical screens, that correspond to the image-taking elements, the step of modifying the at least one virtual position comprises selecting, from the virtual pixel areas on the virtual screen, at least one virtual pixel area including the at least one virtual position, and determining, on the one physical screen, at least one physical pixel area corresponding to the at least one virtual pixel area, and the step of obtaining the at least one optical characteristic value associated with the at least one physical position on the one physical screen comprises obtaining at least one optical characteristic value associated with the at least one physical pixel area on the one physical screen, as at least one optical characteristic value associated with the at least one virtual pixel area on the virtual screen.
In the present image-data processing method, the modifying data associate the respective virtual pixel areas on the virtual screen, with the respective physical pixel areas on each of the physical screen, and the optical characteristic value associated with the physical position on one physical screen is obtained as the optical characteristic value associated with the physical pixel area on the one physical screen. That is, all positions included in each virtual pixel area is associated with the optical characteristic value associated with the physical pixel area corresponding to the each virtual pixel area. Therefore, the degree of resolution on the virtual screen is limited by the size of each physical pixel area. However, in the present method, since a physical pixel area corresponding to a virtual pixel area on the virtual screen is known in advance, the amount of calculations needed to determine a modifying amount to modify a virtual pixel area on the virtual screen may be less than that needed to determine a modifying amount to modify an arbitrary virtual position on the virtual screen. As far as the present feature is concerned, the respective areas of the virtual pixel areas corresponding to the physical pixel areas on the physical screens are equal to each other.
(3) According to a third feature of the present invention that includes the first feature (1), the modifying data comprise a plurality of modifying tables each of which associates a plurality of prescribed sets of coordinates prescribed on the virtual screen, with a plurality of modifying amounts to modify the plurality of prescribed sets of coordinates and thereby determine, on a corresponding one of the physical screens, a plurality of physical sets of coordinates corresponding to the plurality of prescribed sets of coordinates, and the step of modifying the at least one virtual position comprises determining, based on one of the modifying tables that corresponds to the one physical screen, at least one modifying amount corresponding to at least one virtual set of coordinates indicating the at least one virtual position on the virtual screen, and determining, based on the at least one modifying amount, at least one physical set of coordinates corresponding to the at least one virtual set of coordinates, on the one physical screen.
In the image-data processing method according to the second feature (2), a modifying amount is not determined for an arbitrary virtual position, but for a virtual pixel area corresponding to an image-taking element of the image-taking device. In contrast, in the present image-data processing method, it may be assumed that modifying amounts are continuous values and, on this assumption, a modifying amount for an arbitrary virtual set of coordinates is obtained based on a plurality of modifying amounts for a plurality of prescribed sets of coordinates. In the present method, no virtual or physical pixel areas are used as unit, but a modifying amount for an arbitrary virtual set of coordinates is obtained, which leads to improving the accuracy with which the optical characteristic value of the object is obtained. The manner in which a modifying amount for an arbitrary virtual set of coordinates is obtained may be such that a modifying amount is determined based on a modifying amount for the prescribed set of coordinates that is the nearest to the virtual set of coordinates; or such that a modifying amount is determined based on respective modifying amounts for a plurality of neighboring prescribed sets of coordinates that neighbor the virtual set of coordinates, as will described in the following feature (4), below. It is preferred that the prescribed sets of coordinates be uniformly located or distributed on the virtual screen.
(4) According to a fourth feature of the present invention that includes the third feature (3), the step of determining the at least one modifying amount comprises determining the at least one modifying amount corresponding to the at least one virtual set of coordinates, based on the one modifying table which associates a plurality of neighboring prescribed sets of coordinates neighboring the at least one virtual set of coordinates on the virtual screen, with a plurality of modifying amounts to modify the plurality of neighboring prescribed sets of coordinates and thereby determine, on the one physical screen, a plurality of physical sets of coordinates corresponding to the plurality of neighboring prescribed sets of coordinates.
In the present image-data processing method, a modifying amount for an arbitrary virtual set of coordinates is determined based on respective modifying amounts for a plurality of neighboring prescribed sets of coordinates that neighbor the virtual set of coordinates. The thus determined modifying amount enjoys a higher reliability than that determined based on the modifying amount for the prescribed set of coordinates that is the nearest to the virtual set of coordinates.
The total number of the neighboring prescribed sets of coordinates that are selected to determine a modifying amount for one virtual set of coordinates may not be limited. For example, in the case where a modifying amount for an arbitrary virtual set of coordinates is determined based on respective modifying amounts for four neighboring prescribed sets of coordinates that neighbor the virtual set of coordinates, the amount of calculations needed to determine the modifying amount for the arbitrary virtual set of coordinates is not increased so much, while the reliability of the modifying amount determined is improved to a satisfactory level.
(5) According to a fifth feature of the present invention that includes the third or fourth feature (3) or (4), the image-taking device includes a plurality of image-taking elements, and the each batch of object-part-image data comprises the plurality of optical characteristic values which are, on the corresponding physical screen, associated with respective physical pixel areas corresponding to the plurality of image-taking elements of the image-taking device, and the step of obtaining the at least one optical characteristic value associated with the at least one physical position on the one physical screen comprises obtaining at least one optical characteristic value associated with at least one physical pixel area including the at least one physical set of coordinates corresponding to the at least one virtual set of coordinates.
In the present image-data processing method, an optical characteristic value is determined on an image-taking-element basis, i.e., on a pixel-area basis. Therefore, the degree of resolution on the virtual screen is limited by the size of the pixel areas, like in the method according to the second feature (2). However, the amount of calculations can be reduced as such.
(6) According to a sixth feature of the present invention that includes the third or fourth feature (3) or (4), the image-taking device includes a plurality of image-taking elements, and the each batch of object-part-image data comprises the plurality of optical characteristic values which are, on the corresponding physical screen, associated with respective physical-pixel-related sets of coordinates indicating respective positions, in the image-taking device, of respective points representing the plurality of image-taking elements, and the step of obtaining the at least one optical characteristic value associated with the at least one physical position on the one physical screen comprises determining at least one optical characteristic value associated with the at least one physical set of coordinates corresponding to the at least one virtual set of coordinates, based on the physical-pixel-related sets of coordinates, and the optical characteristic values associated therewith, of the one physical screen.
In the present image-data processing method according to the above, fifth feature (5), an optical characteristic value is determined not on a physical-coordinate basis but on an image-taking-element or pixel-area basis. In contrast, in the present image-data processing method, a physical set of coordinates corresponding to an arbitrary virtual set of coordinates is determined and, on the assumption that optical characteristic values are continuous on the physical screen including the determined physical set of coordinates, an optical characteristic value corresponding to the determined physical set of coordinates is determined. In the present method, the respective points representing the image-taking elements (hereinafter, reference to as the xe2x80x9cpixel-area-representing pointsxe2x80x9d; and the respective positions of the pixel-area-representing points will be referred to as the xe2x80x9cpixel-area positionsxe2x80x9d) may be determined at anywhere in the corresponding pixel areas on each physical screen, preferably at the respective centers of the pixel areas. It is rational that the optical characteristic value obtained as the average of all possible values in each pixel area by the is corresponding image-taking element is regarded as the optical characteristic value obtained at the center of the each pixel area. Since the present method assures that an optical characteristic value associated with an arbitrary physical set of coordinates is obtained, it can enjoy a higher accuracy of processing of image data than the method in which image data are processed on a pixel-area basis. It is preferred that the an optical characteristic value associated with a physical set of coordinates be determined based on respective positions of a plurality of pixel-area-representing points neighboring the physical set of coordinates and a plurality of optical characteristic values associated with those positions, as recited in the following seventh feature (7). (7) According to a seventh feature of the present invention that includes the sixth feature (6), the step of determining the at least one optical characteristic value associated with the at least one physical set of coordinates comprises determining the at least one optical characteristic value associated with the at least one physical set of coordinates, based on a plurality of neighboring physical-pixel-related sets of coordinates neighboring the at least one physical set of coordinates, and a plurality of optical characteristic values associated with the plurality of neighboring physical-pixel-related sets of coordinates, of the one physical screen.
In the present method, since an optical characteristic value associated with a physical set of coordinates is determined based on a plurality of neighboring physical-pixel-related sets of coordinates neighboring the physical set of coordinates and a plurality of optical characteristic values associated with the plurality of neighboring physical-pixel-related sets of coordinates, the accuracy of determination of optical characteristic value or values is improved. In the case where an optical characteristic value associated with a physical set of coordinates is determined by proportional calculations of four optical characteristic values respectively associated with four neighboring physical-pixel-related sets of coordinates, the accuracy can be improved without increasing the amount of calculations so much. However, it is possible to determine an optical characteristic value associated with a physical set of coordinates, as a value which is determined on a free curved surface based on nine optical characteristic values respectively associated with nine neighboring physical-pixel-related sets of coordinates.
(8) According to an eighth feature of the present invention that includes any one of the first to seventh features (1) to (7), the image-data processing method further comprises the step of determining, in advance, the one of the physical screens that is to be used to obtain the at least one optical characteristic value associated with the at least one physical position corresponding to the at least one virtual position.
Regarding the overlapping portion of the second object-part image, a physical position may be determined on not only the second physical screen corresponding to the second object-part image but also the first physical screen corresponding to the first object-part image. Since a physical position is determined by modifying a virtual position based on the modifying data, a substantially equal optical characteristic value is obtained by determining the physical position on either the first or second physical screen. The present image-data processing method determines, in advance, which one of the physical screens is used to obtain an optical characteristic value associated with a physical position corresponding to each virtual position designated on the virtual screen. A boundary line is provided in an overlapping portion of the first and second physical screens that corresponds to the overlapping portion of the second object-part image, for example, is defined by a straight line which perpendicularly and equally divides a straight line segment connecting the respective centers of the first and second object-part images.
(9) According to a ninth feature of the present invention that includes any one of the first to eighth features (1) to (8), the image-taking device includes a plurality of image-taking elements, and the overlapping portion of the second object-part image has a width which is not smaller than twice a width of a physical pixel area corresponding to each of the image-taking elements.
The overlapping portion must not include a position for which an optical characteristic value cannot be obtained from either the first or second physical screen. Hence, it is desirable that the overlapping portion have a width or dimension not smaller than twice a width or dimension of a physical pixel area corresponding to each of the image-taking elements. However, the size of xe2x80x9ctwicexe2x80x9d is selected on the assumption that an optical characteristic value associated with a physical set of coordinates is determined based on four optical characteristic values respectively associated with four pixel-area-related sets of coordinates neighboring the physical set of coordinates. Therefore, in the case where an optical characteristic value associated with a physical set of coordinates is determined based on more optical characteristic values respectively associated with more pixel-area-related sets of coordinates neighboring the physical set of coordinates, the overlapping portion needs to have a greater width. In the latter case, it is preferred that the width of the overlapping portion be about ten times greater than that of each pixel area. Meanwhile, in the case where the modifying data are produced using a standard substrate having a plurality of reference marks regularly provided thereon, as will be described later, it is preferred that the width of the overlapping portion be sufficiently greater than a width of each reference mark.
(10) According to a tenth feature of the present invention that includes any one of the first to ninth features (1) to (9), the object comprises a connector.
The present image-data processing method may be carried out for an EC mounting apparatus which mounts a connector as an object on a circuit substrate. In this case, part images of the connector are taken and, based on image data representing the part images, a condition of the connector may be inspected.
(11) According to an eleventh feature of the present invention, there is provided an image-data processing system, at least one image-taking device which takes a plurality of object-part images from a plurality of parts of an object, respectively, the object-part images imaging the parts of the object such that at least one first object-part image images at least one first part and at least one second object-part image images at least one second part adjacent to the at least one first part and includes at least one overlapping portion imaging a portion of the at least one first part; an object-part-image-data memory which stores a plurality of batches of object-part-image data representing the plurality of object-part images taken by the image-taking device, each of the batches of object-part-image data comprising a plurality of optical characteristic values respectively associated with a plurality of physical positions, and thereby defining a corresponding one of a plurality of physical screens; a modifying-data memory which stores predetermined modifying data; and a virtual-data producing device which modifies, based on the modifying data, at least one virtual position on a virtual screen corresponding to the parts of the object, and thereby determines at least one physical position corresponding to the at least one virtual position, on one of the physical screens, and which produces virtual data comprising the at least one virtual position which is, on the virtual screen, associated with at least one optical characteristic value which is, on the one physical screen, associated with the at least one physical position.
The present image-data processing system may carry out the image-data processing method according to the first feature (1). The physical position may be a physical pixel area corresponding to each of a plurality of image-taking elements of the image-taking device, and the virtual position may be a virtual pixel area corresponding to the physical pixel area. Alternatively, the virtual position may be an arbitary virtual position on the virtual screen, and the physical position may be a physical position corresponding to the arbitrary virtual position, on one of the physical screens, as will be described later.
The present system may employ any one of the first to tenth features (1) to (10).
(12) According to a twelfth feature of the present invention that includes the eleventh feature (11), the virtual-data producing device modifies, based on the modifying data, at least one virtual set of coordinates representing the at least one virtual position, and thereby determines at least one physical set of coordinates corresponding the at least one virtual set of coordinates, and produces the virtual data comprising the at least one virtual set of coordinates which is, on the virtual screen, associated with the at least one optical characteristic value which is, on the one physical screen, associated with the at least one physical set of coordinates.
Like the image-data processing method according to the third feature (3), the present image-data processing system determines a physical set of coordinates corresponding to an arbitrary virtual set of coordinates, and obtains an optical characteristic value associated with the physical set of coordinates. Thus, the present system can obtain a very accurate optical characteristic value of the object. An optical characteristic value associated with a physical set of coordinates may be determined based on an optical characteristic value associated with a physical pixel area including the physical set of coordinates, or based on at least one (preferably, plural) optical characteristic value associated with at least one pixel-area-related set of coordinates neighboring the physical set of coordinates. An optical characteristic value associated with a physical set of coordinates can be more accurately determined based on plural optical characteristic values associated with plural neighboring pixel-area-related sets of coordinates, than a single optical characteristic value associated with a single neighboring pixel-area-related set of coordinates.
(13) According to a thirteenth feature of the present invention, there is provided a method of predetermining the modifying data recited in the eleventh or twelfth feature (11) or (12), comprising the steps of taking, with the at least one image-taking device, at least two substrate-part images from at least two parts of a substrate that correspond to the at least one first part and the at least one second part of the object, the substrate having a plurality of reference marks which are regularly provided on a surface thereof, obtaining at least two batches of substrate-part-image data representing the at least two substrate-part images, respectively, the at least two substrate-part images imaging the at least two parts of the substrate such that at least one first substrate-part image images at least one first part of the substrate and at least one second substrate-part image images at least one second part of the substrate adjacent to the at least one first part in the substrate and includes at least one overlapping portion imaging a portion of the at least one first part of the substrate, each of the at least two batches of substrate-part-image data defining a corresponding one of a plurality of physical screens, and producing, based the on at least two physical screens, and a virtual screen corresponding to the at least two parts of the substrate and having, thereon, respective prescribed positions of the reference marks of the substrate, the modifying data to modify each of respective physical positions of the reference marks on the at least two physical screens so as to coincide with a corresponding one of the prescribed positions of the reference marks on the virtual screen.
The present modifying-data predetermining or producing method can predetermine or produce the modifying data which can modify both the positional errors of the reference marks caused by the distortion of the substrate-part images taken by the image-taking device, and the relative-position errors and relative-angular-phase errors of the image-taking device when the image-taking device takes the substrate-part images. If there are no (or negligible, if any) image distortion, relative-position errors, or relative-angular-phase errors, then each of the respective physical positions of the reference marks on the physical screens should coincide with a corresponding one of the prescribed positions of the reference marks on the virtual screen. However, if there are, the present method produces the modifying data which is used to modify each of the respective physical positions of the reference marks on the physical screens so as to coincide with a corresponding one of the prescribed positions of the reference marks on the virtual screen. The correction data may be so produced as to be continuous within a range corresponding to each of the physical screens, but not continuous at a boundary between the two physical screens corresponding to the first and second substrate-part images.
The modifying data are so predetermined or produced as to be used in the image-data processing method according to any one of the first to tenth features (1) to (10), or in the image-data processing system according to the eleventh or twelfth feature (11) or (12). In other words, as the image-data processing method or system takes the object-part images from the parts of the object, the modifying-data producing method takes the substrate-part images from the parts of the standard substrate, such that the dimensions of each of the first and second parts of the substrate are equal to those of each of the first and second parts of the object, the distance between the first and second parts of the substrate is equal to that of the first and second parts of the object, and the width of the overlapping portion of the second substrate-part image is equal to that of the second object-part image.
However, the standard substrate having the reference marks is not necessarily required to have such dimensions that are not smaller than the total dimensions of all the parts of the object from which the image-taking device takes the object-part images. If the substrate has those dimensions, then the number of substrate-part images that is needed to produce the modifying data corresponding to all of the parts of the object can be advantageously obtained by moving at least one of the substrate and the image-taking device relative to the other, by the corresponding number of times, and operating the image-taking device to take the respective images of the parts of the substrate. However, if the substrate has such dimensions that correspond to the total dimensions of at least two parts of the object, then it is possible to obtain substrate-part images needed to produce the modifying data corresponding to three or more parts of the object. For example, in the case where the object consists of three parts, a standard substrate having dimensions somewhat larger than the total dimensions of two parts of the object, is employed, first, respective images of two parts of the substrate that correspond to a first pair of adjacent parts of the object are taken, so that first modifying data are produced based on the thus taken two substrate-part images, and then the substrate is moved to a position where the two parts of the substrate are opposed to one of the above two parts, and the remaining third part, of the object, that is, a second pair of adjacent parts of the object, so that respective images of the two parts of the substrate are taken and second modifying data are produced based on the thus taken two substrate-part images. The first modifying data can be used commonly for the first pair of parts of the object, and the second first modifying data can be used commonly to the second pair of parts of the object, but neither of the first and second modifying data can be used commonly for the three parts of the object. However, if one of respective half portions of the first and second modifying data that correspond to the middle one of the three parts of the object is subjected to an appropriate coordinate transformation, then the one half portion of one of the first and second modifying data coincides with the other half portion of the other modifying data; and, if the other half portion of the one modifying data is subjected to the coordinate transformation, then third modifying data which can be used commonly for the three parts of the object, are produced.
It is preferred that the reference marks be uniformly distributed over the entire range of the standard substrate that corresponds to all the parts of the object.
(14) According to a fourteenth feature of the present invention that includes the thirteenth feature (13), the step of producing the modifying data comprises producing the modifying data to modify a physical set of coordinates indicating the each of the respective physical positions of the reference marks on the at least two physical screens so as to coincide with a prescribed set of coordinates indicating the corresponding one of the prescribed positions of the reference marks on the virtual screen.
A physical set of coordinates indicating the physical position of each reference mark may be a physical set of coordinates indicating the center of each reference mark. A known image-processing technique, such as the technique disclosed in U.S. Pat. No. 5,754,677, may be utilized to determine the physical set of coordinates indicating the center of each of the reference marks on the physical screens. According to the technique disclosed in the U.S. patent, it is assumed that optical characteristic values obtained from the substrate-part images are continuous values, and a boundary between the image of each reference mark and its background is determined. Thus, the shape of each reference mark can be accurately recognized.
(15) According to a fifteenth feature of the present invention that includes the fourteenth feature (14), the step of producing the modifying data comprises producing a plurality of prescribed sets of coordinates indicating the prescribed positions of the reference marks on the virtual screen, and a plurality of modifying vectors respectively directed from the plurality of prescribed sets of coordinates to a plurality of physical sets of coordinates indicating the respective physical positions of the reference marks on the at last two physical screens, and producing at least two modifying tables each of which associates at least two prescribed sets of coordinates out of the plurality of prescribed sets of coordinates, with at least two modifying vectors out of the plurality of modifying vectors.
The prescribed sets of coordinates indicating the prescribed positions of the reference marks on the virtual screen correspond to the prescribed sets of coordinates prescribed on the virtual screen recited in the third feature (3), and the modifying vectors correspond to the modifying amounts recited in the third feature (3). The modifying tables are produced for the physical screens, respectively.
(16) According to a sixteenth feature of the present invention that includes any one of the thirteenth to fifteenth features (13) to (15), the step of taking the at least two substrate-part images comprises sequentially taking, with a single image-taking device as the at least one image-taking device, the at least two substrate-part images from the at least two parts of the substrate, and the step of producing the modifying data comprises producing, based on at least one of the at least two modifying tables that corresponds to at least one of the at least two physical screens, image-distortion data representing a distortion of the at least one physical screen relative to the virtual screen, and producing positional-error data representing a positional error of each of the at least two physical screens relative to the virtual screen.
In the case where the single image-taking device takes the substrate-part images from the parts of the standard substrate, the errors caused by the distortion of one or more components of the image-taking device (e.g., a lens or a matrix of CCDs), and the modifying amounts to modify or correct the errors, can be considered as being common to all of the physical screens. Hence, the present modifying-data producing method produces the modifying data including the image-distortion data which can be used commonly to all the physical screens, and the positional-error data representing the positional error of each of the physical screens. Thus, the total amount of the modifying data can be reduced as compared with the case where the modifying tables corresponding to the physical screens include respective batches of image-distortion data.
In addition, since the image-distortion data and the positional-error data can be stored in different areas of a memory, the two sorts of data can be utilized independent of each other. For example, in the case where the position of the image-taking device is changed as the operation of the EC mounting apparatus is advanced, the positional-error data may be changed and used while the image-distortion data are not changed.
(17) According to a seventeenth feature of the present invention that includes the sixteenth feature (16), the step of producing the positional-error data comprises producing, based on the modifying vectors of each of the at least two modifying tables, parallel-position-error data representing a position error of a corresponding one of the at least two physical screens relative to the virtual screen in a direction parallel to the virtual screen, and producing, based on the modifying vectors of the each modifying table, angular-phase-error data representing an angular-phase error of the corresponding one physical screen relative to the virtual screen about an axis line perpendicular to the virtual screen.
(18) According to an eighteenth feature of the present invention that includes the sixteenth feature (16), the step of producing the positional-error data comprises producing, based on at least one error of at least one physical set of coordinates indicating the physical position of at least one representative reference mark of the reference marks on the each physical screen, relative to at least one prescribed set of coordinates indicating the prescribed position of the at least one representative reference mark on the virtual screen, parallel-position-error data representing a position error of the each physical screen relative to the virtual screen in a direction parallel to the virtual screen, and producing, based on the at least one error of the at least one physical set of coordinates indicating the physical position of the at least one representative reference mark on the each physical screen, relative to the at least one prescribed set of coordinates indicating the prescribed position of the at least one representative reference mark on the virtual screen, angular-phase-error data representing an angular-phase error of the each physical screen relative to the virtual screen about an axis line perpendicular to the virtual screen.
In the present modifying-data producing method, the parallel-position-error data and the angular-phase-error data can be produced by selecting, as the representative reference mark, a reference mark located in a portion (e.g., a central portion) of each of the physical screens where the each physical screen is less influenced by the image distortion. Thus, the total amount of calculations needed to produce the modifying data can Into be reduced as compared with the method according to the above, eighteenth feature (18).
(19) According to a nineteenth feature of the present invention that includes the sixteenth to eighteenth features (16) to (18), the step of producing the positional-error data further comprises determining, based on the positional-error data and at least one prescribed offset amount prescribed for the at least two physical screens, a physical offset amount between the at least two physical screens.
The physical offset amount may be determined for each pair of adjacent physical screens of the at least two physical screens, based on a corresponding pair of modifying tables of the at least two modifying tables. Alternatively, the physical offset amount may be determined for an appropriate one pair of adjacent physical screens of the at least two physical screens and may be regarded as being equal to that for each other pair of adjacent physical screens.
(20) According to a twentieth feature of the present invention that includes the nineteenth feature (19), the at least two physical screens comprise a single main physical screen and at least one auxiliary physical screen, and wherein the step of determining the physical offset amount comprises determining a relative positional error of the at least one auxiliary physical screen relative to the main physical screen.
The present modifying-data producing method determines the relative positional error of the auxiliary physical screen relative to the main physical screen. Therefore, the modifying table corresponding to the main physical screen may include the image-distortion data, and the modifying table corresponding to the auxiliary physical screen may not include the image-distortion data.
(21) According to a twenty-first feature of the present invention that includes the twentieth feature (20), the step of obtaining the at least two batches of substrate-part-image data comprises obtaining at least three batches of substrate-part-image data representing at least three substrate-part images taken from at least three parts of the substrate, and defining at least three physical screens, respectively, and the at least three physical screens comprise the main physical screen representing an middle one of the at least three substrate-part images taken from a middle one of the at least three parts of the substrate.